This invention relates to axle suspension systems of the type that have beam assemblies, pivotally connected to opposite sides of a vehicle frame, so that they move about a given point. An axle which carries ground-engaging wheels is secured to the beam assemblies, and an air bag or similar system is disposed in load-transmitting relation between the assemblies and the frame at the end of the beam opposite the pivot connection. More particularly, this invention relates to certain unique pivotal connections between the beam assembly and the vehicle frame, that also serve to keep axles properly aligned, with respect to the longitudinal axis of the vehicle.
It is known, in beam type suspension systems, to make use of a system including turnbuckles, adjusting screws, eccentric pins or similar devices, to initially align and subsequently adjust the alignment of the axle relative to the frame, as well as maintain a pivotal connection between the beam and the vehicle frame. In each of these cases, some type of bolt, clamp or equivalent device has been used to lock the pivot connection between a beam assembly and frame bracket in a stationary position. As a result, the axle, which is connected to the beam assembly, is also locked in a stationary position relative to the longitudinal axis of the beam assembly, once it is determined that the axle is in proper alignment relative to the frame. Conventionally, the pivot connection locking device has been entirely or partially comprised of manually releasable threaded elements, to facilitate adjustment of the axle alignment, as may be required from time to time during the life of the vehicle.
Exemplary of the prior art vehicle suspension beam pivot connections are U.S. Pat. Nos. 3,960,388 to Strader, Masser and Lundwall, Re 30,308 to Masser, and U.S. Pat. No. 4,166,640 to VanDenberg. The Masser patents disclose a vehicle beam suspension system, having a pivotal connection between the control arm and the frame, wherein the frame bracket has a slotted aperture substantially longer than the diameter of a connecting bolt that passes through them, in order to provide fore and aft adjustment of the control arm and, therefore, alignment of the axle connected to it. The connecting bolt is used to initially fix the alignment of the axle by tensioning the mounting plates against the frame brackets at a desired position. The mounting plates are then welded to the frame brackets, to further fix the alignment of the suspension system relative to the vehicle frame. The axle alignment can subsequently be adjusted by loosening the bolt and breaking the weld. U.S. Pat. No. 4,166,640 to VanDenberg discloses a pivot connection structure that connects a vehicle suspension beam assembly to a vehicle frame. This pivot connection structure uses a bolt to maintain the connection, and also requires rigid metal-to-metal contact between the pin of the connection and the hanger bracket.
While the alignment technique of U.S. Pat. No. 4,166,640 has proven highly advantageous, it and the other techniques have the disadvantage of usually requiring a manually releasable locking means, such as a bolt, which the vehicle operator must torque to as high as about 800 ft. lbs.), once the axle is properly aligned, in order to secure the beam to the vehicle frame. Such torques are not always conveniently achievable by the operator. In addition, the existence of a manually releasable locking means is an undesirable invitation, to an operator or someone maintaining the vehicle, to continually adjust the alignment of the axle using the beam pivot connection.
Known beam pivot/axle alignment connections have also generally required extra parts, such as bushings and heavy bolts, to resist sheer forces generated by such systems. These additional parts add weight and cost to the suspension system and, therefore, reduce the maximum permissible load that can be carried in jurisdictions where that weight is limited. Many prior art connections have also depended largely upon metal-to-metal contact in the area of the connection. Due to the rigid, or quasi-rigid, connection between the axle and the beam assemblies of some of these systems, many of the articulation forces encountered by the vehicle wheels are translated along the beam to the beam pivot connection. These forces can cause a subsequent wearing of the metal parts in contact with one another and, perhaps more importantly, potentially loosen the manually releasable locking means.
It is known to try to take up the deflections in suspensions caused by articulation forces during operation, by providing a resilient bushing construction that is integral with the beam, such as that which is taught in VanDenberg U.S. Pat. No. 4,166,640. The unique resilient bushing construction taught in that patent has met with tremendous commercial success, due in large measure to the longevity of the bushing. Removal of the bushing construction may be necessary to service the axle or brakes of the vehicle. Also, while the resilient bushing construction of this patent is extraordinarily long-lived, it may, during the life of the vehicle, need to be replaced, or if another resilient bushing construction is used, the bushing may require more frequent replacement. Known hanger bracket constructions have closed slots in their side walls. Existing hanger bracket constructions, therefore, do not facilitate rebushing of a beam having an integral bushing construction, where one of the components of the bushing is longer than the width of hanger bracket, so the ends of the bushing extend beyond the side walls of the bracket. Furthermore, existing beam pivot/axle alignment connections do not allow for replacement of the resilient bushing in the beam assembly, while still insuring proper axle alignment after rebushing of the beam has been completed.